Elements. Remove from AugmentedInterfaceElement 'interfaces' and 'mixins'.

Change-Id: I95d4d11c0a5b0a5ccbfe7890f87cf3836a7a39f9
Reviewed-on: https://dart-review.googlesource.com/c/sdk/+/414182
Reviewed-by: Brian Wilkerson <brianwilkerson@google.com>
Commit-Queue: Konstantin Shcheglov <scheglov@google.com>

https://dart.googlesource.com/sdk/+/6a7fd7cedb6e6aa4d0548f59071ac381f66bc340

DEPS

diff --git a/DEPS b/DEPS
index 34518e2..933c4d4 100644
--- a/DEPS
+++ b/DEPS
@@ -234,7 +234,7 @@
 ]
 
 deps = {
-  'flutter/engine/src/flutter/third_party/dart': Var('dart_git') + '/sdk' + '@' + 'e52b1416609208b058ae3bfca9e8b5496a2ae54b',
+  'flutter/engine/src/flutter/third_party/dart': Var('dart_git') + '/sdk' + '@' + '6a7fd7cedb6e6aa4d0548f59071ac381f66bc340',
 
   'flutter': Var('flutter_git') + '/mirrors/flutter' + '@' + '8876bccf3ab8cbdd8cb65a53f911ca658830209d',
 

commits.json

diff --git a/commits.json b/commits.json
index a0118b0..62aba93 100644
--- a/commits.json
+++ b/commits.json
@@ -1,4 +1,4 @@
 {
   "flutter":"8876bccf3ab8cbdd8cb65a53f911ca658830209d",
-  "flutter/engine/src/flutter/third_party/dart":"e52b1416609208b058ae3bfca9e8b5496a2ae54b"
+  "flutter/engine/src/flutter/third_party/dart":"6a7fd7cedb6e6aa4d0548f59071ac381f66bc340"
 }
\ No newline at end of file